Apparatus for reducing polymer deposition on a substrate and substrate support

ABSTRACT

An adjustable RF coupling ring is capable of reducing a vertical gap between a substrate and a hot edge ring in a vacuum processing chamber. The reduction of the gap reduces polymer deposits on the substrate and electrostatic chuck and improves wafer processing.

FIELD OF THE INVENTION

[0001] The invention relates to an apparatus and method for reducingpolymer deposition on a substrate and substrate support, and moreparticularly, the invention relates to the adjustment of a gap between asubstrate holder and a substrate to reduce polymer deposition on exposedsurfaces of the substrate holder and bottom surfaces of the substrate.

DESCRIPTION OF THE RELATED ART

[0002] Vacuum processing chambers are generally used for chemical vapordepositing (CVD) and etching of materials on substrates by supplyingprocess gas to the vacuum chamber and application of an RF field to thegas. Examples of parallel plate, inductively coupled plasma (TCP™, alsocalled ICP), and electron-cyclotron resonance (ECR) reactors aredisclosed in commonly owned U.S. Pat. Nos. 4,340,462; 4,948,458; and5,200,232. The substrates are held in place within the vacuum chamberduring processing by substrate holders. Conventional substrate holdersinclude mechanical clamps and electrostatic clamps (ESC). Examples ofmechanical clamps and ESC substrate holders are provided in commonlyowned U.S. Pat. No. 5,262,029 and commonly owned U.S. Pat. No.5,671,116. Substrate holders in the form of an electrode can supplyradio frequency (RF) power into the chamber, as disclosed in U.S. Pat.No. 4,579,618.

[0003] Substrates which are etched in an oxide etching process generallyinclude an underlayer, an oxide layer which is to be etched, and aphotoresist layer formed on top of the oxide layer. The oxide layer maybe one of SiO₂, BPSG, PSG, or other oxide material. The underlayer maybe Si, TiN, suicide, or other underlying layer or substrate material.During processing of substrates, unwanted polymer deposition on thesurfaces of the chamber can occur. For instance, when the chamber heatsup to above 80° C. during oxide etching, a reaction can occur whereinCF₃ forms CF₂ and HF. The formation of CF₂ leads to an increase inpolymer deposition on surfaces within the chamber.

[0004] During etching of a substrate such as a semiconductor wafer in aplasma reactor, the polymer can build up on the cooled, exposed surfacesof the chamber including exposed surfaces of a substrate support such asan electrostatic chuck and other surfaces such as a dielectric annularcap/focus ring surrounding the substrate support. This buildup may causeproblems if it flakes off and is carried onto the top surface of theelectrostatic chuck. These contaminants on the top surface of the chuckcan prevent the chuck from operating properly to hold the wafersecurely. In addition, the contaminants can allow helium which issupplied under the wafer as a cooling medium to leak from beneath thewafer and reduce the wafer cooling. The contaminants can also bedeposited on and adversely affect the wafer itself.

[0005] The buildup of polymer can be removed by a cleaning stepperformed between the processing of successive wafers. Generally,cleaning can be performed by injecting oxygen into the chamber, strikinga plasma and reacting the oxygen with the deposited polymer to achievean aggressive oxygen clean of the processing chamber.

[0006] The aggressive oxygen cleaning of the processing chamber isundesirable because it adds to the wafer cycle time, reducingthrough-put of the system. In addition, the aggressive oxygen clean willshorten the lives of members within the processing chamber due to ionbombardment of these members. As such, it would be desirable ifsubstrate processing could be carried out without a need for theaggressive oxygen cleaning step to thereby shorten cycle time and extendthe life of chamber components.

[0007] One example of a vacuum processing chamber 10 is illustrated inFIG. 1. The vacuum processing chamber 10 includes a substrate holder 12including an electrode providing an RF bias to a substrate supportedthereon. The substrate holder 12 includes an electrostatic clamp 14 forclamping the substrate. The substrate which is placed on theelectrostatic clamp 14 is preferably cooled by helium backcooling (notshown) provided between the substrate and the electrostatic clamp. Aring 16 surrounds the electrostatic clamp 14. The ring 16 may be aceramic focus ring; a combination of a focus ring, coupling ring, andedge ring; or another combination of rings.

[0008] The vacuum processing chamber 10 includes a source of energy formaintaining a high density (e.g. 10¹¹-10¹² ions/cm³) plasma in thechamber such as an antenna 18 (such as a planar spiral coil or othersuitable design) which is positioned above the chamber and powered by asuitable RF source. A suitable RF impedance matching circuit,inductively couples RF into the chamber 10 so as to provide a highdensity plasma. The chamber 10 also includes a suitable vacuum pumpingapparatus for maintaining the interior of the chamber at a desiredpressure (e.g. below 50 mTorr, typically 1-20 mTorr). A dielectricwindow 20 (such as a uniformly thick and planar sheet of quartz,alumina, silicon nitride, etc.) is provided between the antenna 18 andthe interior of the processing chamber 10 and forms the vacuum chamberwall at the top of the processing chamber 10. A dielectric gasdistribution plate, commonly called a showerhead 22, may be providedbeneath the window 20 and includes a plurality of openings such ascircular holes (not shown) for delivering process gas supplied by a gassupply to the processing chamber 10. However, the gas distribution plate22 can be omitted and process gas can be supplied to the chamber byother arrangements such as gas rings, etc.

[0009] One area in which deposits of polymer can occur in a processingchamber is a narrow gap 30 between the wafer supported on theelectrostatic chuck 14 and the surrounding ring(s) 16. Specifically, agap 30 is provided beneath the edge of the wafer which overhangs thesurrounding ring. This gap 30 allows for manufacturing tolerances,thermal expansion and wear of the parts. However, process gas andvolatile byproducts within the chamber 10 may migrate into the gap 30and cause undesirable polymer deposits in the gap and on the undersideedge of the wafer which may flake off and cause contamination of thewafer and/or chamber.

[0010]FIG. 2 is an enlarged cross sectional view of an outer portion ofan electrostatic chuck 14′ and surrounded rings including a focus ring16, a coupling ring 40, and a hot edge ring 42.

[0011] As shown in the enlarged view of FIG. 3, when a substrate S inthe form of a semiconductor wafer is positioned on the electrostaticchuck 14′ and held in place by a suitable electrostatic clamping force asmall vertical gap 30′ is provided between an overhanging edge of thesubstrate S and a groove 44 provided in the edge of the hot edge ring42. This vertical clearance gap 30′ is designed to prevent theoverhanging edge of the substrate S from being lifted and thereby avoida reduction in clamping force applied by the electrostatic chuck 14′.However, this additional vertical clearance gap 30′ provides additionalopportunity for polymer buildup which may flake off and contaminate thesubstrate S or the electrostatic chuck 14′.

[0012] Thus, it would be desirable to reduce the vertical gap 30′between the hot edge ring 42 or other surrounding ring and theoverhanging substrate edge.

SUMMARY OF THE INVENTION

[0013] The present invention relates to an apparatus for adjusting a gapbetween a ring surrounding substrate support and a substrate.

[0014] In accordance with one aspect of the invention the plasmaprocessing apparatus comprises a processing chamber, a power sourcewhich energizes process gas in an interior of the processing chamberinto a plasma state for processing a substrate, a substrate supportwhich supports a substrate within the interior of the processingchamber, the substrate support having an upper surface, an upper ringsurrounding the substrate support, the upper ring having a portionextending under a substrate when the substrate is located on thesubstrate support, and a coupling ring surrounding the substratesupport, the coupling ring having a first ring rotatable with respect toa second ring to adjust height of the coupling ring and adjust a gapbetween the upper ring and the substrate.

[0015] In accordance with another aspect of the invention the plasmaprocessing apparatus comprises a processing chamber, a process gas whichenergizes process gas in an interior of the processing chamber into aplasma state for processing a substrate, a substrate support whichsupports a substrate within the interior of the processing chamber, thesubstrate support having an upper surface, an upper ring surrounding thesubstrate support, the upper ring having a portion extending under asubstrate when the substrate is located on the substrate support, and acoupling ring surrounding the substrate support, the coupling ringhaving a first ring rotatable with respect to a second ring to adjustheight of the coupling ring and adjust a gap between the upper ring andthe substrate.

[0016] In accordance with a further aspect of the invention the methodof reducing polymer deposition on a substrate support in a plasmaprocessing system comprises providing an adjustment mechanism foradjusting a gap between a substrate and a surrounding ring in a plasmaprocessing apparatus, and adjusting the gap between the substrate andthe surrounding ring by rotating a first ring with respect to a secondring of the adjustment mechanism.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0017] The invention will now be described in greater detail withreference to the preferred embodiments illustrated in the accompanyingdrawings, in which like elements bear like reference numerals, andwherein:

[0018]FIG. 1 is a cross sectional view of a vacuum processing chamber;

[0019]FIG. 2 is an enlarged cross sectional view of a portion of FIG. 1showing the electrostatic chuck and surrounding rings;

[0020]FIG. 3 is an enlarged cross sectional view of portion A of FIG. 2;

[0021]FIG. 4 is an enlarged cross sectional view of a portion of avacuum processing chamber according to the present invention includingan adjustable coupling ring;

[0022]FIG. 5 is an exploded schematic prospective view of the adjustablecoupling ring of FIG. 4; and

[0023]FIG. 6 is an enlarged cross sectional view of a portion of anelectrostatic chuck and focus ring showing a gap between the focus ringand substrate.

DETAILED DESCRIPTION OF THE INVENTION

[0024] A portion of a substrate support for a vacuum processing chamberaccording to one embodiment of the present invention is illustrated inFIG. 4. The substrate support 100 illustrated in FIG. 1 includes anelectrostatic chuck 102, a focus ring 104, a coupling ring 106, and ahot edge ring 108.

[0025] As is well known to those familiar with the plasma processingart, the rings surrounding the electrostatic chuck including the focusring 104, coupling ring 106, and hot edge ring 108 help focus the ionsfrom the RF induced plasma region on the surface of the substrate toimprove process uniformity, particularly at the edge of the substrate.This is because when RF power is supplied to substrate holding chuck102, equipotential field lines are set up over substrate and bottomelectrode. These field lines are not static but change during the RFcycle. The time averaged field results in the bulk plasma being positiveand the surface of the substrate and electrostatic chuck negative. Dueto geometry factors, the field lines are not uniform at the edge of thesubstrate. The focus, coupling, and hot edge rings help direct the bulkof the RF coupling through substrate to the overlying plasma by actingas a capacitor between the plasma and the powered electrode (e.g.,RF-powered chuck ).

[0026] The hot edge ring 108 overlays an adjustable RF coupling ring106. The hot edge ring 108 is a sacrificial edge ring surrounding theelectrostatic chuck 102. The hot edge ring 108 is a replaceablecomponent which tends to become hot during processing of a substrate andthus is referred to as a hot edge ring. The hot edge ring 180 may bemade from conductive electrode materials such as SiC and silicon or fromdielectric materials such as quartz. By changing the edge ring material,the degree of coupling through the plasma can be tailored to provide adesired localized “edge” etch rate at the outer portion of a substratebeing processed. SiC, having a lower capacitive impedance, willgenerally produce a faster edge etch rate than silicon. Quartz and otherdielectrics will have a lesser effect on the edge etch rate.

[0027] In the described embodiment a gap 130, shown in FIG. 6, is formedbetween an over hanging edge of the substrate S and the silicon hot edgering 108. The gap 130 has a vertical dimension d controlled by theadjustable RF coupling ring 106. The adjustable RF coupling ring 106 iscapable of controlling the vertical dimension d of the gap by moving thesilicon hot edge ring 108 in a vertical direction as appropriate. Itshould be noted that vertical direction is any direction substantiallyparallel to a Y axis, as shown in FIGS. 1 and 6.

[0028] In accordance with one embodiment of the invention, theadjustable RF coupling ring 106 moveably supports the silicon hot edgering 108. The adjustable RF coupling ring 106 provides mechanicalsupport for the silicon hot edge ring 108 as well as the capability tocontrol the gap distance d to within a specified range. In one aspect ofthe invention, the adjustable RF coupling ring 106 is capable of formingthe gap with an associated gap distance d ranging between approximately0.5 mils to less than 6 mils.

[0029] In the described embodiment, the adjustable RF coupling ring 106includes two rings 110, 112 as shown in FIG. 5. The first ring 110 ortop ring includes three projections 114 extending from the ring in adirection parallel to a Y axis of the ring. The second ring 112 orbottom ring includes three sets of a plurality of graduated steps 116around the circumference of the ring. Rotation of the first ring 110clockwise with respect to the second ring 112 decreases an overallvertical height of the coupling ring 106 and adjusts the gap between thesubstrate and the hot edge ring 108.

[0030] In the described embodiment, the adjustable coupling ring 106preferably includes graduated steps 116 that vary in height incrementsof about 0.0001-0.01 inches and preferably about 0.001 inches. Althoughthe illustrated embodiment includes six graduated steps 116 in each ofthe three sets of steps, other numbers of steps may also be useddepending on the amount of adjustment and graduation of adjustmentdesired. According to another embodiment twelve graduated steps 116 areprovided for twelve adjustment heights.

[0031] In the described embodiment, the top ring 110 of an adjustablecoupling ring 106 includes the projections 114 with a height which isequal to approximately the total height of all the steps 116 in one ofthe three sets of plurality of graduated steps. In a preferredembodiment, the projections 114 have a height of about 0.012 inches. Inthe described embodiment, the adjustable coupling ring 106 can be formedof quartz.

[0032] The adjustable RF coupling ring 106 according to the presentinvention, allows the precise adjustment of the gap 130 between thesubstrate S and the hot edge ring 108 in a plurality of individualsteps. The coupling ring 106 allows an operator to readjust the couplingring at any time between processing of substrates or during set up ofthe vacuum processing chamber. The RF coupling ring 106 also ensuresthat the hot edge ring 108 is adjusted evenly on all sides of thesubstrate and that a top surface of the coupling ring remainssubstantially horizontal.

[0033] The adjustable RF coupling ring 106 may be installed in newvacuum processing chambers or used to retrofit existing vacuumprocessing chambers to provide adjustability of the hot edge ring 108.

[0034] A process for installing and adjusting the adjustable RF couplingring 106 is easily implemented as follows. The bottom ring 112 of thecoupling ring 106 is placed on the step of the electrostatic chuck 102with the plurality of graduated steps 116 facing upward. The top ring110 is then placed onto the bottom ring 112 with the three projections114 each aligned on the highest of the graduated steps. The hot edgering 108 is then placed on top of the assembled coupling ring 106 andthe gap is measured with a measuring device. One example of a measuringdevice is a vertical mount dial indicator which is placed on thesubstrate holding chuck 102 and measures a vertical distance from thetop of the chuck to the top of the edge of the hot edge ring 108.Preferably, the gap 130 is measured at 90 degrees apart around theelectrostatic chuck. The measurement is taken at a location on the hotedge ring 108 close to the electrostatic chuck 102. Due to deteriorationor wear of the hot edge ring, just outside the edge of the substrate,the area of the hot edge ring 108 closest to the chuck 102 should be thehighest location in the hot edge ring groove. The measurement willgenerally indicate that the hot edge ring 108 is higher than theelectrostatic chuck 102 and that the hot edge ring needs to be adjusteddownward. The hot edge ring 108 is then removed. The coupling ring 106is then adjusted by rotating the top ring 110 clockwise and thusreducing the height of the coupling ring. The hot edge ring 18 is thenreplaced and the adjustment is then repeated until a minimum gapdistance d is achieved.

[0035] According to one preferred embodiment of the invention, the rings110 and 112 of the coupling ring 106 include a locking feature (notshown) which locks the rings in an aligned radial position. One exampleof a locking mechanism includes an detent on the top ring 110 whichinterlocks with grooves on each step of the bottom coupling ring 112.

[0036] It should be appreciated that in a specific system, the specificshape of the focus ring 104, the coupling ring 106, and the hot edgering 108 may vary depending on the arrangement of chuck 102, substrateand/or others. Therefore, the exact shape of the rings surrounding thechuck in FIGS. 4-6 are shown for illustration purposes only and are notlimiting in any way. Although the invention has been illustrated with acoupling ring arranged to adjust a hot edge ring, other rings may alsobe adjusted using the coupling ring.

[0037] While the invention has been described in detail with referenceto the preferred embodiments thereof, it will be apparent to one skilledin the art that various changes and modifications can be made andequivalents employed, without departing from the present invention.

What is claimed is:
 1. A plasma processing apparatus comprising: aprocessing chamber; a power source which energizes process gas in aninterior of the processing chamber into a plasma state for processing asubstrate; a substrate support which supports a substrate within theinterior of the processing chamber, the substrate support having anupper surface; an upper ring surrounding the substrate support, theupper ring having a portion extending under a substrate when thesubstrate is located on the substrate support; and a coupling ringsurrounding the substrate support, the coupling ring having a first ringrotatable with respect to a second ring to adjust height of the couplingring and adjust a gap between the upper ring and the substrate.
 2. Theapparatus of claim 1, wherein the coupling ring is arranged to adjust adistance between a lower surface of the substrate and an upper surfaceof the portion of the upper ring extending under the substrate byrotation of the first ring with respect to the second ring.
 3. Theapparatus of claim 1, wherein the upper ring is a hot edge ring.
 4. Theapparatus of claim 1, wherein the second ring comprises a plurality ofstepped surfaces.
 5. The apparatus of claim 4, wherein the coupling ringcomprises: a first ring having at least three projections extending fromthe ring in a direction parallel to an axis of the ring; and a secondring having at least three sets of a plurality of steps arranged toreceive each of the at least three projections, wherein a totalthickness of the first and second ring is adjustable by rotation of thefirst ring with respect to the second ring.
 6. The apparatus of claim 5,wherein the steps each have a height of about 0.001 inches.
 7. Theapparatus of claim 1, wherein substrate support comprises anelectrostatic chuck.
 8. An adjustment mechanism for adjusting a gapbetween a substrate and a focus ring in a plasma processing apparatus,the adjustment mechanism comprising: a first ring having at least threeprojections extending from the ring in a direction parallel to an axisof the ring; and a second ring having at least three sets of a pluralityof steps arranged to receive each of the at least three projections,wherein a total thickness of the first and second ring is adjustable byrotation of the first ring with respect to the second ring.
 9. Theadjustment mechanism of claim 8, wherein the steps each have a height ofabout 0.001 inches.
 10. A method of reducing polymer deposition on asubstrate support in a plasma processing system comprising: providing anadjustment mechanism for adjusting a gap between a substrate and asurrounding ring in a plasma processing apparatus; and adjusting the gapbetween the substrate and the surrounding ring by rotating a first ringwith respect to a second ring of the adjustment mechanism.
 11. Themethod of claim 10, wherein the surrounding ring is a hot edge ring. 12.The method of claim 11, wherein the adjustment mechanism is placedbetween a focus ring and the hot edge ring.